Can I get a Chinese business/tourist visa up to 6 months?

I guess it is hard for you to get a business or tourist visa for up to 6 months. Nigerian applicants are very hard to get a China visa. If you want to get a business visa, you have to get an official invitation letter issued by Chinese government department’ companies and social organizations authorized by the Chinese Foreign Ministry, such as Bureau of Foreign Trade and Economic Cooperation, Foreign Affairs Office. You can't get it in person, you have to have a host company or organization to help you to get the invitation letter.

For tourist visa, I think you have to show an invitation letter issued by a qualified international travel agency. It is not easy for you to get a tourist visa, either. You'd better enquire the embassy in person because the rule for Nigerians is so strict.